Ceramic plate for a semiconductor producing/inspecting apparatus

ABSTRACT

An object of the present invention is to provide a ceramic plate comprising a ceramic substrate for a semiconductor producing/examining device making it possible to prevent a warp of its ceramic substrate from being generated and prevent damage and the like of a silicon wafer put on the ceramic substrate, based on the warp, from being generated. The ceramic plate for a semiconductor producing/examining device of the present invention is a ceramic plate comprising a ceramic substrate for a semiconductor producing/examining device, a semiconductor wafer being put on a surface of the ceramic substrate, or held a given distance apart from the surface of the above-mentioned ceramic substrate, wherein the surface roughness of the ceramic substrate according to JIS R 0601 is set as follows: Rmax=0.1 to 250 μm, and the surface roughness of the wafer-putting/holding face of the above-mentioned ceramic substrate is equal to that of the face opposite to the wafer-putting/holding face, or a difference between the surface roughness of the wafer-putting/holding face and that of the face opposite to the wafer-putting/holding face is 50% or less.

TECHNICAL FIELD

[0001] The present invention relates to a ceramic plate used mainly in asemiconductor producing/examining device, particularly to a ceramicplate for a semiconductor producing/examining device which a large-sizedsilicon wafer can be put on and which does not cause any damage of awafer and the like.

BACKGROUND ART

[0002] Semiconductors are very important products necessary in variousindustries. A semiconductor chip is produced, for example, by slicing asilicon monocrystal into a given thickness to produce a silicon wafer,and then forming various circuits etc. on this silicon wafer.

[0003] In such a process for producing semiconductor chips, there arewidely used semiconductor producing/examining devices using, as a basethereof, a ceramic substrate such as an electrostatic chuck, a hotplate, a wafer prober, a susceptor and the like.

[0004] As such semiconductor producing/examining devices, for example,Japanese Patent gazette No. 2587289 and the publication of JP Kokai Hei10-72260 disclose ceramic substrates used for these purpose.

[0005] All of the ceramic substrates disclosed in the above-mentionedpublications and so on have a diameter of about 6 inches (150 mm) or athickness of 8 mm or more.

[0006] However, as silicon wafers have been made large-sized in recentyears, ceramic substrates having a diameter of 8 inches or more havebeen required.

[0007] In the process for producing a silicon wafer, it is necessary touse a ceramic substrate in which heating elements are embedded so as toheat the wafer. Furthermore, in order to make the heat capacity thereofsmall to improve the temperature following character thereof, it hasbeen required to make the thickness thereof less than 10 mm.

[0008] According to the publication of JP Kokai Hei 7-280462, in thisceramic heater, the surface roughness of a face on which a silicon waferis put or above which a silicon wafer is held to keep a given intervalbetween the face and the wafer (referred to as a wafer-putting/holdingface hereinafter) according to JIS R 0601 is set as follows: Rmax=lessthan 2 μm. The above-mentioned surface roughness of the face oppositethereof is adjusted to a roughness sufficient to cause diffusedreflection of heat rays, that is Rmax=2 to 200 μm.

SUMMARY OF THE INVENTION

[0009] However, when such a ceramic heater wherein heating elements areformed on a large-sized and thin ceramic substrate on which rougheningtreatment was carried out was utilized, a problem that a warp isgenerated at a high temperature range arose.

[0010] Thus, a cause that such a problem arose was investigated. As aresult, it has been found out that the cause is based on the followingmechanism.

[0011] In this ceramic heater, the surface roughness of thewafer-putting/holding face is smaller than that of the face opposite tothe wafer-putting/holding face. Therefore, if Young's modulus thereofdrops at high temperature, the face opposite to thewafer-putting/holding face, the roughness of which is larger, becomessomewhat easily extended. As a result, a warp is generated.

[0012] Also, in the case that the surface roughness of both main facesof the ceramic substrate is too large, even if the surface roughness ofthe wafer-putting/holding face is made equal to that of the faceopposite to the wafer-putting/holding face, the wafer-putting/holdingface contracts more easily and thus a warp is generated. On the otherhand, if the surface roughness is made very small to make the face flat,conditions for grinding or blast treatment must be made harsh. For thisreason, stress based on grinding treatment and the like remains on thesurface of the ceramic substrate, and thus, a warp is rather easilygenerated since this stress is released at high temperature.

[0013] The inventors conducted research repeatedly in order to solvesuch a problem about the generation of a warp of a ceramic substrate. Asa result, it has been found out that by adjusting the surface roughnessof both main faces of a ceramic substrate into a given range andadjusting a difference in the surface roughness between itswafer-putting/holding face and the face opposite to thewafer-putting/holding face to 50% or less, the generation of a warp inthe ceramic substrate can be prevented. Thus, the present invention hasbeen completed.

[0014] That is, the present invention is a ceramic plate comprising aceramic substrate for a semiconductor producing/examining device,wherein a semiconductor wafer is put on a surface of the ceramicsubstrate, or is held a given distance apart from the surface of theceramic substrate, wherein:

[0015] the surface roughness of the above-mentioned ceramic substrateaccording to JIS R 0601 is set as follows: Rmax=0.1 to 250 μm; and

[0016] the surface roughness of the wafer-putting/holding face of theabove-mentioned ceramic substrate is equal to the surface roughness ofthe face opposite to the wafer putting/holding face, or a differencebetween the surface roughness of the wafer-putting/holding face and thesurface roughness of the face opposite to the wafer-putting/holding faceis 50% or less.

[0017] In the above-mentioned ceramic plate for a semiconductorproducing/examining device, the above-mentioned ceramic substrate ispreferably in a disc form and has a diameter of 200 mm or more and athickness of 50 mm or less.

BRIEF DESCRIPTION OF DRAWINGS

[0018]FIG. 1 is a plan view that schematically illustrates a ceramicheater, which is one example of the ceramic plate for a semiconductorproducing/examining device of the present invention.

[0019]FIG. 2 is a sectional view that schematically illustrates a partof the ceramic heater illustrated in FIG. 1.

[0020]FIG. 3 is a longitudinal sectional view that schematicallyillustrates an electrostatic chuck, which is one example of the ceramicplate for a semiconductor producing/examining device of the presentinvention.

[0021]FIG. 4 is a sectional view taken on A-A line of the electrostaticchuck illustrated in FIG. 3.

[0022] FIGS. 5(a) to (d) are sectional views that schematicallyillustrate a process for manufacturing the electrostatic chuck.

EXPLANATION OF SYMBOLS

[0023]10 ceramic heater

[0024]11 heater plate

[0025]11 a wafer-putting/holding face

[0026]11 b bottom face

[0027]12 heating element

[0028]12 a metal covering layer

[0029]13 external terminal

[0030]14 bottomed hole

[0031]15 through hole

[0032]16 supporting pin

[0033]19 silicon wafer

[0034]20 chuck positive electrostatic layer

[0035]30 chuck negative electrostatic layer

[0036]20 a, 30 a connecting electrode

[0037]20 b, 30 b combteeth-shaped electrode

[0038]40 ceramic dielectric film

[0039]50 resistance heating element

[0040]100 ceramic substrate

[0041]101 electrostatic chuck

DETAILED DISCLOSURE OF THE INVENTION

[0042] The ceramic plate comprising a ceramic substrate for asemiconductor producing/examining device, wherein a semiconductor waferis put on a surface of the above-mentioned ceramic substrate, or is helda given distance apart from the surface of the above-mentioned ceramicsubstrate,

[0043] wherein:

[0044] the surface roughness of the above-mentioned ceramic substrateaccording to JIS R 0601 is set as follows: Rmax=0.1 to 250 μm; and

[0045] the surface roughness of the wafer-putting/holding face of theabove-mentioned ceramic substrate is equal to the surface roughness ofthe face opposite to the above-mentioned wafer-putting/holding face, ora difference between the surface roughness of the wafer-putting/holdingface and the surface roughness of the above-mentioned face opposite tothe above-mentioned wafer-putting/holding face is 50% or less.

[0046] The difference in the surface roughness in the presentspecification is a value calculated by the following equation (1):

Difference (%) in the surface roughness=[(larger surfaceroughness−smaller surface roughness)/larger surface roughness]×100  (1)

[0047] Therefore, in the ceramic plate for a semiconductorproducing/examining device of the present invention, the surfaceroughness of the wafer-putting/holding face may be larger, or thesurface roughness of the face opposite to the wafer-putting/holding facemay be larger.

[0048] In the present invention, firstly, the surface roughness of theceramic substrate according to JIS R 0601 is adjusted as follows:Rmax=0.1 to 250 μm; therefore, there do not arise problems as describedin the part of prior art, that is, problems that thewafer-putting/holding face contracts easily or stress remains in thesurface. Furthermore, the surface roughness of the wafer-putting/holdingface may be adjusted equal to that of the face opposite to thewafer-putting/holding face, or a difference between the surfaceroughness of the wafer-putting/holding face and that of the faceopposite to the wafer-putting/holding face is adjusted to be 50% orless; therefore, no warp owing to the fact that the difference in thesurface roughness is too large is generated.

[0049] Particularly, the difference in the surface roughness isoptimally 20% or less. By setting the difference in the surfaceroughness to 20% or less, the warp amount of the disc-form ceramicsubstrate having a diameter of 200 mm or less can be set to 5 μm orless. As a result, the heating property of a semiconductor wafer can beimproved and an examination error of a wafer prober can be removed.Moreover, the chuck power of an electrostatic chuck can be improved.

[0050] Consequently, even if the silicon wafer or the like is put onthis ceramic plate for a semiconductor producing/examining device and isthen heated, the silicon wafer is not damaged on the basis of any warp.

[0051] The ceramic substrate used in the present invention desirably hasa diameter of 200 mm or more and a thickness of 50 mm or less. This isbecause semiconductor wafers having a diameter of 8 inches or morebecome the main current and it is required to make semiconductor waferslarge-sized.

[0052] In ceramic substrates having a large diameter of 8 inches ormore, a warp at high temperature is more easily generated, and with thissize, the structure of the present invention works effectively.

[0053] The diameter of the above-mentioned ceramic substrate is moredesirably 12 inches (300 mm) or more. This is because this is a sizewhich will become the main current of semiconductor wafers of the nextgeneration.

[0054] The reason why the thickness of the above-mentioned ceramicsubstrate is preferably 50 mm or less is that if the thickness is over50 mm, the heat capacity of the ceramic substrate becomes large. Thus,if a temperature control means is set up to heat or cool the ceramicsubstrate, the temperature following character becomes deteriorated.

[0055] In the ceramic substrate whose thickness is as small as 50 mm orless, a warp is easily generated at high temperature. As a result, thestructure of the present invention acts effectively.

[0056] The thickness of the ceramic substrate is more preferably 5 mm orless. If the thickness is over 5 mm, the heat capacity thereof becomeslarge so that the temperature controllability and temperature uniformityin the wafer-putting/holding face deteriorate.

[0057] As the ceramic plate of the present invention, it is desired touse a ceramic whose Young's modulus at the temperature range of 25 to800° C. is 280 GPa or more. Such a ceramic is not particularly limited.Examples thereof include nitride ceramics, carbide ceramics and thelike.

[0058] If the Young's modulus is less than 280 GPa, the rigidity is toolow. As a result, it becomes difficult to make the warp amount at thetime of heating small.

[0059] Examples of the nitride ceramics include aluminum nitride,silicon nitride, boron nitride and the like. Examples of the carbideceramics include silicon carbide, zirconium carbide, titanium carbide,tantalum carbide, tungsten carbide and the like.

[0060] In the case that the above-mentioned aluminum nitride is used, asubstance having a composition comprises more than 50% by weight ofaluminum nitride is preferred. Examples of some other ceramics used inthis case include alumina, sialon, silicon carbide, silicon nitride andthe like.

[0061] The Young's modulus of the above-mentioned ceramic substrate canbe controlled by using a mixture or a lamination of two or more kinds ofceramics, or by adding thereto, for example, an alkali metal, an alkaliearth metal, a rare earth metal, carbon and the like. As theabove-mentioned alkali metal or the alkali earth metal, Li, Na, Ca, Rband the like are preferred. As the rare earth metal, Y is preferred. Asthe carbon, amorphous or crystalline carbon may be used. The carboncontent is desirably from 100 to 5000 ppm. Since such content makes itpossible to blacken the ceramic plate.

[0062] In the present invention, a conductor layer may be disposedinside the ceramic substrate and this conductor layer can be caused tofunction as, for example, a heating element, a guard electrode, a groundelectrode, an electrostatic electrode and the like. A conductor layermay be deposited on a surface of the ceramic substrate and thisconductor layer can be caused to function as, for example, a heatingelement, a chuck top electrode and the like.

[0063] Furthermore, plural conductor layers, such as a heating element,a guard electrode and a ground electrode, may be disposed inside theceramic substrate.

[0064] In the case that an electrostatic electrode is set up, theceramic substrate functions as an electrostatic chuck.

[0065] Examples of the material constituting the above-mentionedconductor layer include a metal sintered body, a non-sintered metal bodyand a sintered body of a conductive ceramic.

[0066] As the raw material of the above-mentioned metal sintered bodyand the non-sintered metal body, for example, a high melting point metaland the like can be used. Examples of the above-mentioned high meltingpoint metal include tungsten, molybdenum, nickel, indium and the like.These may be used alone or in combination of two or more.

[0067] Examples of the above-mentioned conductive ceramic includecarbides of tungsten and molybdenum.

[0068] Such a ceramic plate at which a heating element, a guardelectrode, a ground electrode and so on are set up, may be used as, forexample, a hot plate (a ceramic heater), an electro static chuck, awafer prober and the like.

[0069]FIG. 1 is a plan view that schematically shows an example of aceramic heater that is one embodiment of the ceramic plate for asemiconductor producing/examining device of the present invention. FIG.2 is a partially enlarged cross section view that schematically shows apart of the above-mentioned ceramic heater.

[0070] A ceramic substrate 11 is made in a disk form. Heating elements12 are made in the pattern of concentric circles on the bottom face ofthe ceramic substrate 11, in order to heat the wafer-putting/holdingface of the ceramic substrate 11 so as to make the temperature of thewhole of the wafer-putting/holding face uniform.

[0071] About these heating elements 12, two concentric circles near toeach other, as a pair, are connected so as to produce one line, andexternal terminal pins 13, which will be inputting/outputting terminalpins, are connected to both ends thereof. Through holes 15, into whichsupporting pins 16 will be inserted, are made in an area near thecenter. Moreover, bottomed holes 14, into which temperature-measuringelements will be inserted, are made.

[0072] As shown in FIG. 2, the supporting pins 16, on which a siliconwafer 19 can be put and can be moved up and down. By the supportingpins, the silicon wafer 19 can be delivered to a non-illustrated carriermachine or the silicone wafer 19 can be received from the carriermachine.

[0073] The heating elements 12 may be formed inside the ceramicsubstrate 11 and at the center thereof or at positions biased from thecenter toward the wafer-putting/holding face.

[0074] Examples of the pattern of the resistance heating elements 12include concentric circuits, a spiral, eccentric circuits, and windinglines and the like. The pattern in the form of concentric circuits, asillustrated in FIG. 1, is preferred since the pattern makes it possibleto make the temperature of the whole of the heater plate uniform.

[0075] In order to form the heating elements 12 inside the ceramicsubstrate or on the bottom face of the ceramic substrate, it is desiredto use a conductor containing paste made of a metal or a conductiveceramic.

[0076] That is, in the case that the heating elements are formed insidethe ceramic substrate, the resistance heating elements are made by:forming a conductor containing paste on a green sheet; and subsequentlylaminating and firing such green sheets. On the other hand, in the casethat the heating elements are formed on the surface, the heatingelements are usually made by performing firing to manufacture a ceramicsubstrate, forming a conductor containing paste layer on a surfacethereof, and firing the resultant.

[0077] The above-mentioned conductor containing paste is notparticularly limited, and is preferably a paste comprising not onlymetal particles or a conductive ceramic for keeping electricalconductivity but also a resin, a solvent, a thickener and so on.

[0078] The above-mentioned metal particles are preferably made of, forexample, a noble metal (gold, silver, platinum or palladium), lead,tungsten, molybdenum, nickel and the like. These may be used alone or incombination of two or more. These metals are relatively hard to beoxidized, and have a resistance value sufficient for generating heat.

[0079] Examples of the above-mentioned conductive ceramic includecarbides of tungsten and molybdenum. These may be used alone or incombination of two or more. The particle diameter of these metalparticles or the conductive ceramic particles is preferably from 0.1 to100 μm. If the particle diameter is too fine, that is, less than 0.1 μm,they are easily oxidized. On the other hand, if the particle diameter isover 100 μm, they are not easily sintered so that the resistance valuebecomes large.

[0080] The shape of the above-mentioned metal particles may be sphericalor scaly. When these metal particles are used, they may be a mixture ofspherical particles and scaly particles.

[0081] In the case that the above-mentioned metal particles are made ofscaly particles or a mixture of spherical particles and scaly particles,a metal oxide between the metal particles is easily retained andadhesiveness between the heating elements 12 and a nitride ceramic andthe like is secured. Moreover, the resistance value can be made large.Thus, this case is profitable.

[0082] Examples of the resin used in the conductor containing pasteinclude epoxy resins, phenol resins and the like. Examples of thesolvent are isopropyl alcohol and the like. Examples of the thickenerare cellulose and the like.

[0083] In the above-mentioned conductor containing paste, a metal oxideis preferably added to the metal particles, and the heating elements 12are desirably made up to a sintered body of the metal particles and themetal oxide, as described above. By sintering the metal oxide togetherwith the metal particles in this way, the nitride ceramic, which is theceramic substrate, can be closely adhered to the metal particles.

[0084] The reason why the adhesiveness to the nitride ceramic and thelike is improved by mixing the above-mentioned metal oxide is unclear,but would seem to be based on the following. The surface of the metalparticles or the surface of the nitride ceramic is slightly oxidized sothat an oxidized film is formed thereon. Pieces of this oxidized filmare sintered and integrated with each other through the metal oxide sothat the metal particles and the nitride ceramic and the like areclosely adhered to each other.

[0085] As an example of the metal oxide, at least one selected from thegroup consisting of lead oxide, zinc oxide, silica, boron oxide (B₂O₃),alumina, yttria, and titania is preferable.

[0086] These oxides make it possible to improve adhesiveness between themetal particles and the nitride ceramic without increasing theresistance value of the heating elements 12.

[0087] When the total amount of the metal oxides is adjusted to 100parts by weight, the weight ratio of lead oxide, zinc oxide, silica,boron oxide (B₂O₃), alumina, yttria and titania is as follows: leadoxide: 1 to 10, silica: 1 to 30, boron oxide: 5 to 50, zinc oxide: 20 to70, alumina: 1 to 10, yttria: 1 to 50 and titania: 1 to 50. The ratio ispreferably adjusted within the scope that the total thereof is not over100 parts by weight.

[0088] By adjusting the amounts of these oxides within these ranges, theadhesiveness to the nitride ceramic can be particularly improved.

[0089] The addition amount of the metal oxide to the metal particles ispreferably 0.1% by weight or more and less than 10% by weight. The arearesistivity when the conductor containing paste having such a structureis used to form the heating elements 12 is preferably from 1 to 45 mΩ/□.

[0090] If the area resistivity is over 45 mΩ/□, the calorific value foran applied voltage becomes too large so that in the ceramic substrate 11wherein heating elements 12 are set on its surface their calorific valueis not easily controlled. If the addition amount of the metal oxide is10% or more by weight, the area resistivity exceeds 50 mΩ/□ so that thecalorific value becomes too large. Thus, temperature control becomesdifficult so that uniformity of temperature distribution deteriorates.

[0091] In the case that the heating elements 12 are formed on thesurface of the ceramic substrate 11, a metal covering layer 12 a ispreferably formed on the surface of the heating elements 12, asillustrated in FIG. 2. The metal covering layer prevents a change in theresistance value based on oxidization of the inner metal sintered body.The thickness of the formed metal covering layer 12 a is preferably from0.1 to 10 μm.

[0092] The metal used when the metal covering layer 12 a is formed isnot particularly limited if the metal is non-oxidizable. Specificexamples thereof include gold, silver, palladium, platinum, nickel andthe like. These may be used alone or in combination of two or more.Among these metals, nickel is preferred.

[0093] In the present invention, thermocouples may be embedded in theceramic substrate if necessary. With the thermocouples, the temperatureof the heating elements is measured, and on the basis of the datavoltage or electric current amount is changed to control thetemperature.

[0094] The size of the connecting portions of metal wires of thethermocouples is the same as the strand diameter of the respective metalwires or more, and the size is preferably 0.5 mm or less. Such astructure makes the heat capacity of the connecting portion small, andcauses temperature to be correctly and speedy converted to an electriccurrent value. For this reason, temperature controllability is improvedso that temperature distribution in the heated surface of the waferbecomes small.

[0095] Examples of the above-mentioned thermocouple include K, R, B, S,E, J and T type thermocouples, as described in JIS-C-1602 (1980).

[0096] Next, the following will describe the process for manufacturingthe ceramic plate for a semiconductor producing/examining device of thepresent invention.

[0097] First, a process for manufacturing the ceramic plate wherein theheating elements 12 are formed on the bottom face of the ceramicsubstrate 11 shown in FIG. 1 will be described.

[0098] (1) Step of forming the ceramic plate

[0099] A slurry is prepared by blending powder of a nitride ceramic,such as the above-mentioned aluminum nitride with, if necessary, asintering aid such as yttria, a binder and so on. Thereafter, thisslurry is made into a granular form by spray-drying and the like. Thegranule is put into a mold and pressed to be formed into a plate formand the like form. Thus, a raw formed body (green) is formed.

[0100] Next, portions which will be the through holes 15, into which thesupporting pins 16 for supporting a silicon wafer will be inserted, andportions which will be the bottomed holes 14, into whichtemperature-measuring elements such as thermocouples will be embeddedare made in the raw formed body if necessary.

[0101] Next, this raw formed body is heated and fired to be sintered.Thus, a plate made of the ceramic is manufactured. Thereafter, the plateis made into a given shape to manufacture the ceramic substrate 11. Theshape of the raw formed body may be such a shape that the sintered bodycan be used as it is. By heating and firing the raw formed body underpressure, the ceramic substrate 11 having no pores can be manufactured.It is sufficient that the heating and the firing are performed atsintering temperature or higher. The heat firing temperature is from1000 to 2500° C. for the nitride ceramic.

[0102] (2) Step of printing a conductor containing paste on the ceramicsubstrate

[0103] A conductor containing paste is generally a fluid comprisingmetal particles, a resin and a solvent, and has a high viscosity. Thisconductor containing paste is printed in portions where heating elementsare to be arranged by screen printing and the like, to form a conductorcontaining paste layer. Since it is necessary that the heating elementsmake the temperature of the whole of the ceramic substrate uniform, theconductor containing paste is desirably printed into a pattern ofconcentric circles, as shown in FIG. 1.

[0104] The conductor containing paste layer is desirably formed in sucha manner that a section of the heating elements 12 subjected to thefiring will be rectangular and flat.

[0105] (3) Firing of the conductor containing paste

[0106] The conductor containing paste layer printed on the bottom faceof the ceramic substrate 11 is heated or fired to remove the resin andthe solvent and sinter the metal particles. Thus, the metal particlesare baked onto the bottom face of the ceramic substrate 11 to form theheating elements 12. The heating and firing temperature is preferablyfrom 500 to 1000° C.

[0107] If the above-mentioned metal oxide is added to the conductorcontaining paste, the metal particles, the ceramic substrate and themetal oxide are sintered to be integrated with each other. Thus, theadhesiveness between the heating elements and the ceramic substrate isimproved.

[0108] (4) Forming a metal covering layer

[0109] A metal covering layer 12 a is desirably deposited on the surfaceof the heating elements 12 (reference to FIG. 2). The metal coveringlayer 12 a can be formed by electroplating, electroless plating,sputtering and the like. From the viewpoint of mass-productivity,electroless plating is optimal.

[0110] (5) Fitting of terminals and so on

[0111] External terminals 13 for connection to a power source are fittedup to ends of the pattern of the heating elements 12 with solder.Thermocouples are inserted into the bottomed holes 14. The bottomedholes are sealed with a heat resistant resin, such as a polyimide, or aceramic, so as to manufacture the ceramic heater 10.

[0112] The following will describe a process for manufacturing a ceramicplate wherein heating elements are formed inside a ceramic substrate.

[0113] (1) Step of forming the ceramic substrate

[0114] First, powder of a nitride ceramic is mixed with a binder, asolvent and so on to prepare a paste. This is used to form a greensheet.

[0115] As the above-mentioned ceramic powder, aluminum nitride, and thelike can be used. If necessary, a sintering aid such as yttria and thelike may be added.

[0116] The amount of yttria is preferably 5% or more by weight. This isbecause 1% or more by weight of yttrium can be caused to remain in thesintered body and the Young's modulus thereof can be adjusted to 280 GPaor more in the temperature range of 25 to 800° C.

[0117] In the case that the remaining amount of yttrium is less than 1%by weight, the Young's modulus thereof is less than 280 GPa at about 25°C. Thus, this case is unfavorable.

[0118] As the binder, desirable is at least one selected from an acrylicbinder, ethylcellulose, butylcellusolve, and polyvinyl alcohol.

[0119] As the solvent, desirable is at least one selected fromα-terpineol and glycol.

[0120] A paste obtained by mixing these is formed into a sheet form bydoctor blade process, to produce a green sheet.

[0121] The thickness of the green sheet is preferably from 0.1 to 5 mm.

[0122] Next, the following are made in the resultant green sheet ifnecessary: portions which will be through holes into which supportingpins for supporting a silicon wafer will be inserted; portions whichwill be bottomed holes in which temperature-measuring elements such asthermocouples will be embedded; portions which will be conductor-filledthrough holes for connecting the heating elements to external terminalpins; and the like. After a green sheet lamination that will bedescribed later is formed, the above-mentioned processing may beperformed.

[0123] (2) Step of printing a conductor containing paste on the greensheet

[0124] A metal paste or a conductor containing paste containing aconductive ceramic is printed on the green sheet.

[0125] This conductor containing paste contains metal particles orconductive ceramic particles.

[0126] The average particle diameter of tungsten particles or molybdenumparticles is preferably from 0.1 to 5 μm. If the average particle isless than 0.1 μm or over 5 μm, the conductor containing paste is noteasily printed.

[0127] Such a conductor containing paste may be a composition (paste)obtained by mixing, for example, 85 to 87 parts by weight of the metalparticles or the conductive ceramic particles; 1.5 to 10 to parts byweight of at least one binder selected from acrylic binders,ethylcellulose, butylcellusolve and polyvinyl alcohol; and 1.5 to 10parts by weight of at least one solvent selected from α-terpineol andglycol.

[0128] (3) Step of laminating the green sheets

[0129] Green sheets on which no conductor containing paste is printedare laminated on the upper and lower sides of the green sheet on whichthe conductor containing paste is printed.

[0130] At this time, the number of the green sheets laminated on theupper side is made larger than that of the green sheets laminated on thelower side to cause the position where the heating elements are formedto be biased toward the bottom face.

[0131] Specifically, the number of the green sheets laminated on theupper side is preferably from 20 to 50, and that of the green sheetslaminated on the lower side is preferably from 5 to 20.

[0132] (4) Step of firing the green sheet lamination

[0133] The green sheet lamination is heated and pressed to sinter thegreen sheets and the inner conductor containing paste.

[0134] Heating temperature is preferably from 1000 to 2000° C., andpressing pressure is preferably from 10 to 20 MPa (100 to 200 kg/cm²).The heating is performed in the atmosphere of an inert gas. As the inertgas, argon, nitrogen and the like can be used.

[0135] After the firing, bottomed holes into which temperature-measuringelements will be inserted may be made. The bottomed holes can be made bydrilling or blast treatment such as sandblast after surface-grinding.Terminals are connected to the conductor-filled through holes for theconnection of the inside heating elements, and are heated and reflowed.Heating temperature is suitably from 90 to 110° C. in the case oftreatment with solder. The heating temperature is suitably from 900 to1100° C. in the case of treatment with brazing material.

[0136] Furthermore, thermocouples and the like as temperature-measuringelements are fixed with a heat-resistant resin to obtain a ceramicheater.

BEST MODE FOR CARRYING OUT THE INVENTION

[0137] The present invention will be described in more detailedhereinafter.

EXAMPLE 1 Ceramic Heater

[0138] (1) The following paste was used to conduct formation by a doctorblade method, to obtain green sheets 0.47 mm in thickness: a pasteobtained by mixing 100 parts by weight of aluminum nitride powder (madeby Tokuyama Corp., average particle diameter: 1.1 μm), 4 parts by weightof yttria (average particle diameter: 0.4 μm), 11.5 parts by weight ofan acrylic binder, 0.5 part by weight of a dispersant and 53 parts byweight of alcohol comprising 1-butanol and ethanol.

[0139] (2) Next, this green sheet was dried at 80° C. for 5 hours, andsubsequently through holes having a diameter of 1.8 mm, 3.0 mm and 5.0mm were made by punching. These through holes were portions which wouldbe through holes into which supporting pins for supporting a siliconwafer would be inserted; and portions which would be conductor-filledthrough holes; and so on.

[0140] (3) The following were mixed to prepare a conductor containingpaste A: 100 parts by weight of tungsten carbide particles having anaverage particle diameter of 1 μm, 3.0 parts by weight of an acrylicbinder, 3.5 parts by weight of α-terpineol solvent, and 0.3 part byweight of a dispersant.

[0141] The following were mixed to prepare a conductor containing pasteB: 100 parts by weight of tungsten particles having an average particlediameter of 3 μm, 1.9 parts by weight of an acrylic binder, 3.7 parts byweight of α-terpineol solvent, and 0.2 part by weight of a dispersant.

[0142] This conductor containing paste A was printed on the green sheetby screen printing, so as to form a conductor containing paste layer forheating elements. The printed pattern was a concentric circular patternas illustrated in FIG. 1. Thirty-seven green sheets on which no printingprocessing was performed were stacked on the upper side (heating faceside) of the green sheet subjected to the above-mentioned processing,and the same thirteen green sheets were stacked on the lower side of thegreen sheet. The resultant was pressed and integrated at 130° C. andunder a pressure of 8 MPa (80 kg/cm²) to form a lamination.

[0143] The conductor containing paste B was filled into the through holeportions which would be the conductor-filled through holes.

[0144] (4) Next, the resultant lamination was degreased at 600° C. inthe atmosphere of nitrogen gas for 5 hours and hot-pressed at 1890° C.and under a pressure of 15 MPa (150 kg/cm²) for 10 hours to obtain analuminum nitride plate having a thickness of 3 mm. This was cut off intoa disk form having a diameter of 300 mm to prepare a ceramic heaterhaving heating elements therein having a thickness of 6 μm and a widthof 10 mm. Next, sandblast treatment of blowing SiC having an averageparticle diameter of 2.5 μm against both faces thereof was conducted, tomake the surface roughness of the wafer-putting/holding face: Rmax=2 μmand that of the opposite face: Rmax=2.3 μm according to JIS B 0601,respectively.

[0145] About the size of the conductor-filled through holes, thediameter thereof was 0.2 mm and the depth thereof was 0.2 mm.

[0146] (5) Next, the plate obtained in the above-mentioned (4) wasground with a diamond grindstone. Subsequently, a mask was put thereon,and bottomed holes 14 for thermocouples were made in the surface byblast treatment with SiC and the like.

[0147] (6) Furthermore, blind holes having a diameter of 5 mm and adepth of 0.5 mm were made by drilling. Brazing gold made of Ni—Au (Au:81.5% by weight, Ni: 18.4% by weight, and impurities: 0.1% by weight)was used, heated and reflowed at 970° C. to connect external terminalsmade of kovar to the blind holes.

[0148] The external terminals were made to have a structure of beingsupported and connected by means of three metal layers comprisingtungsten.

[0149] (7) Next, thermocouples for controlling temperature were buriedin the bottomed holes to finish the production of a ceramic heater.

EXAMPLE 2

[0150] (1) A composition made of 100 parts by weight of aluminum nitridepowder (average particle diameter: 1.1 μm), 4 parts by weight of yttria(average particle diameter: 0.4 μm), 12 parts by weight of an acrylicbinder and an alcohol was subjected to spray-drying to make granularpowder.

[0151] (2) Next, this granular powder was put into a mold and formedinto a flat plate form to obtain a raw formed body (green).

[0152] (3) The raw formed body subjected to the working treatment washot-pressed at 1800° C. and under a pressure of 20 MPa (200 kg/cm²) toobtain a nitride aluminum plate body having a thickness of 3 mm.

[0153] Next, this plate was cut out into a disk having a diameter of 300mm, and then sandblast treatment of blowing alumina particles having anaverage particle diameter of 5 μm against both faces thereof wasconducted, to make the surface roughness of the wafer-putting/holdingface: Rmax=7 μm and that of the opposite face: Rmax=7.5 μm according toJIS B 0601, respectively.

[0154] Furthermore, this formed body was drilled to make portions whichwould be through holes 15 into which supporting pins for a semiconductorwafer would be inserted, and portions (diameter: 1.1 mm, depth: 2 mm)which would be bottomed holes 14 into which thermocouples would beembedded.

[0155] (4) A conductor containing paste was printed on the platesubjected to the above-mentioned treatment (3) by screen printing. Theprinted pattern was a concentric circular pattern as illustrated in FIG.1.

[0156] The used conductor containing paste was Solvest PS603D made byTokuriki Kagaku Kenkyu-sho, which is used to form conductor-filledthrough holes in print circuit boards.

[0157] This conductor containing paste was a silver-lead paste andcontained 7.5 parts by weight of metal oxides made of lead oxide (5% byweight), zinc oxide (55% by weight), silica (10% by weight), boron oxide(25% by weight) and alumina (5% by weight) per 100 parts by weight ofsilver. The silver particles had an average particle diameter of 4.5 μm,and were scaly.

[0158] (5) Next, the heater plate 11 on which the conductor containingpaste was printed was heated and fired at 780° C. to sinter silver andlead in the conductor containing paste and bake them onto the heaterplate 11. Thus, heating elements 12 were formed. The silver-lead heatingelements had a thickness of 5 μm, a width of 2.4 mm and an arearesistivity of 7.7 mΩ/□.

[0159] (6) The heater plate 11 formed in the above-mentioned (5) wasimmersed into an electroless nickel plating bath consisting of anaqueous solution containing 80 g/L of nickel sulfate, 24 g/L of sodiumhypophosphite, 12 g/L of sodium acetate, 8 g/L of boric acid, and 6 g/Lof ammonium chloride to precipitate a metal covering layer (nickellayer) 12 a having a thickness of 1 μm on the surface of the silver-leadheating elements 12.

[0160] (7) By screen printing, a silver-lead solder paste (made byTanaka Kikinzoku Kogyo K. K.) was printed on portions onto whichexternal terminal 13 for attaining connection to a power source would beset up, to form a solder layer.

[0161] Next, external terminals 13 made of Kovar were put on the solderlayer, heated and reflowed at 420° C. to attach the external terminals13 onto the surface of the heating elements.

[0162] (8) Thermocouples for controlling temperature were fixed with apolyimide to obtain a ceramic heater 10.

EXAMPLE 3 Production of an Electrostatic Chuck (Reference to FIGS. 3 to5)

[0163] (1) The following paste was used to conduct formation by a doctorblade method, to obtain green sheets 0.47 mm in thickness: a pasteobtained by mixing 100 parts by weight of aluminum nitride powder (madeby Tokuyama Corp., average particle diameter: 1.1 μm), 4 parts by weightof yttria (average particle diameter: 0.4 μm), 11.5 parts by weight ofan acrylic binder, 0.5 part by weight of a dispersant, 0.2 part byweight of saccharose and 53 parts by weight of alcohol comprising1-butanol and ethanol.

[0164] (2) Next, this green sheet was dried at 80° C. for 5 hours, andsubsequently portions which would be through holes into whichsemiconductor wafer supporting pins having a diameter of 1.8 mm, 3.0 mmand 5.0 mm would be inserted, and portions which would beconductor-filled through holes for attaining connection to externalterminals were made.

[0165] (3) The following were mixed to prepare a conductor containingpaste A: 100 parts by weight of tungsten carbide particles having anaverage particle diameter of 1 μm, 3.0 parts by weight of an acrylicbinder, 3.5 parts by weight of α-terpineol solvent, and 0.3 part byweight of a dispersant.

[0166] The following were mixed to prepare a conductor containing pasteB: 100 parts by weight of tungsten particles having an average particlediameter of 3 μm, 1.9 parts by weight of an acrylic binder, 3.7 parts byweight of α-terpineol solvent, and 0.2 part by weight of a dispersant.

[0167] This conductor containing paste A was printed on the green sheetby screen printing, so as to form a conductor containing paste layer.The printed pattern was a concentric circular pattern. A conductorcontaining paste layer of an electrostatic electrode pattern having theshape illustrated in FIG. 4 was formed on other green sheets.

[0168] The conductor containing paste B was filled into the throughholes for conductor-filled through holes for connecting externalterminals.

[0169] Thirty four green sheets 500′ on which no tungsten paste wasprinted were stacked on the upper side (heating face side) of the greensheet 500 on which the pattern of the resistance heating elements wasformed, and the same thirteen green sheets were stacked on the lowerside of the green sheet. One green sheet 500 on which the conductorcontaining paste layer of the electrostatic electrode pattern wasprinted was stacked thereon, and further two green sheets 500′ on whichno tungsten paste was printed were stacked thereon. The resultant waspressed at 130° C. and under a pressure of 8 MPa (80 kg/cm²) to form alamination (FIG. 5(a)).

[0170] (4) Next, the resultant lamination was degreased at 600° C. inthe atmosphere of nitrogen gas for 5 hours and hot-pressed at 1890° C.and under a pressure of 15 MPa (150 kg/cm²) for 3 hours to obtain analuminum nitride plate having a thickness of 3 mm. This was cut off intoa disk having a diameter of 230 mm to prepare a plate made of aluminumnitride and having therein resistance heating elements 50 having athickness of 6 μm and a width of 10 mm and chuck positive electrostaticlayer 20 and chuck negative electrostatic layer 30 having a thickness of10 μm (FIG. 5(b)).

[0171] (5) Next, the plate obtained in the above-mentioned (4) wasground with a diamond grindstone. Subsequently a mask was put thereon,and bottomed holes (diameter: 1.2 mm, and depth: 2.0 mm) forthermocouples were made in the surface by blast treatment with SiC andthe like. The roughness of the ceramic surface at this time was asfollows: Rmax=3 μm.

[0172] The wafer-putting/holding face was ground to make the face asfollows: Rmax=1.5 μm.

[0173] (6) Furthermore, portions in which the conductor-filled throughholes were made were hollowed out to make blind holes 130 and 140 (FIG.5(c)). Brazing gold made of Ni—Au was used, heated and reflowed at 700°C. to connect external terminals made of Kovar 60 and 180 to the blindholes 130 and 140 (FIG. 5(d)).

[0174] About the connection of the external terminals, a structurewherein a support of tungsten is supported at three points is desirable.This is because the reliability of the connection can be kept.

[0175] (7) Next, thermocouples for controlling temperature were buriedin the bottomed holes to finish the production of an electrostatic chuckhaving the resistance heating elements.

[0176] In the finished electrostatic chuck (FIG. 3), the heater(resistance heating element) pattern 50 and the positive and negativechuck electrostatic layers (electrostatic electrodes) 20 and 30 wereembedded in the ceramic substrate 100. As illustrated in FIG. 4, as thepositive and negative chuck electrostatic layers (electrostaticelectrodes) 20 and 30, combteeth-shaped electrodes 20 b and 30 bconfront each other and connecting electrodes 20 a and 30 a forelectrically connecting the combteeth-shaped electrodes exist.

[0177] A ceramic dielectric film 40 having a thickness of about 300 μmwas formed on the positive and negative chuck electrostatic layer(electrostatic electrodes) 20 and 30. The thickness of ceramicdielectric film 40 can be set into the range of 50 to 2000 μm.

EXAMPLE 4

[0178] The same manufacturing process as in Example 3 was performed.However, both faces of the ceramic substrate 100 were subjected tosandblast treatment in the (5), and the surface roughness of both faceswas made as follows: Rmax=3 μm.

COMPARATIVE EXAMPLE 1

[0179] In the present Comparative Example, an aluminum nitride plate wasobtained in the same way as in the (1) to (4) of Example 1. Thereafter,sandblast treatment of blowing SiC particles having an average particlediameter of 0.5 μm against the wafer-putting face was conducted. On theother hand, sandblast treatment of blowing SiC particles having anaverage particle size of 5 μm against the opposite face was conducted.Thereafter, in the same way as in the (5) to (7) of Example 1, a ceramicheater was obtained.

[0180] The surface roughness of the wafer-putting/holding face of theresultant ceramic heater was: Rmax=1 μm and that of the opposite facewas: Rmax=4.8 μm according to JIS B 0601, respectively.

COMPARATIVE EXAMPLE 2

[0181] In the present Comparative Example, an aluminum nitride plate wasobtained in the same way as in the (1) to (4) of Example 1. Thereafter,sandblast treatment of blowing SiC particles having an average particlediameter of 0.1 μm against both faces thereof was conducted. Thereafter,in the same way as in the (5) to (7) of Example 1, a ceramic heater wasobtained.

[0182] The surface roughness of the wafer-putting/holding face of theresultant ceramic heater was: Rmax=0.08 μm and that of the opposite facewas: Rmax=0.07 μm according to JIS B 0601, respectively.

COMPARATIVE EXAMPLE 3

[0183] In the present Comparative Example, an aluminum nitride plate wasobtained in the same way as in the (1) to (4) of Example 1. Thereafter,sandblast treatment of blowing SiC particles having an average particlediameter of 250 μm against both faces thereof was conducted. Thereafter,in the same way as in the (5) to (7) of Example 1, a ceramic heater wasobtained.

[0184] The surface roughness of the wafer-putting/holding face of theresultant ceramic heater was: Rmax=260 μm and that of the opposite facewas: Rmax=210 μm according to JIS B 0601, respectively.

REFERENCE EXAMPLE

[0185] The same manufacturing process as in Comparative Example 1 wasperformed. However, the diameter was made to 150 mm (6 inches).

Evaluation Method

[0186] The ceramic heaters obtained in Examples 1 and 2 and ComparativeExamples 1 to 3 were heated to 600° C., and then the temperaturesthereof were made return to room temperature. Thereafter, the warpamounts thereof were examined. The warp amounts were measured with adeterminator “Nanoway”, made by Kyocera Corp. The results are shown inTable 1. TABLE 1 Difference (%) in surface roughness between the Warpwafer-putting face and amount the opposite face (μm) Example 1 13 3Example 2 7 3 Example 3 50 6 Example 4 0 2 Comparative 79 10 Example 1Comparative 13 10 Example 2 Comparative 19 10 Example 3 ReferenceExample 79 5

[0187] As shown in Table 1, in the ceramic heaters according to Examples1 and 2, Rmax thereof was within the range of 0.1 to 250 μm, and thedifference in surface roughness between both faces was as small as 13%(Example 1), and 7% (Example 2). Therefore, the warp amount thereof wasas small as 3 μm (Examples 1 and 2). On the other hand, in the ceramicheater according to Comparative Example 1, the difference in surfaceroughness between both faces was as large as 79%; therefore, the warpamount thereof was also as large as 10 μm. In the ceramic heateraccording to Comparative Example 2, the values of the surface roughnessof both faces were too small; therefore, a warp owing to stress wasgenerated and the warp amount was also as large as 10 μm. In the ceramicheater according to Comparative Example 3, the values of the surfaceroughness of both faces were too large; therefore, the warp amount wasas large as 10 μm.

[0188] In the case that the diameter is less than 200 mm as seen inReference Example, a warp is hardly generated.

Industrial Applicability

[0189] As described above, according to the ceramic plate for asemiconductor producing/examining device of the present invention, thesurface roughness of both main faces of its ceramic substrate isadjusted into the above-mentioned given range and the difference insurface roughness between its wafer-putting/holding face and theopposite face is adjusted to 50% or less; therefore, it is possible toprevent the generation of a warp of the ceramic substrate and thegeneration of damage and the like of a silicon wafer based on this warp.

1. A ceramic plate comprising a ceramic substrate for a semiconductor producing/examining device, wherein a semiconductor wafer is put on a surface of said ceramic substrate, or is held a given distance apart from the surface of said ceramic substrate, wherein: the surface roughness of said ceramic substrate according to JIS R 0601 is set as follows: Rmax=0.1 to 250 μm; and the surface roughness of the wafer-putting/holding face of said ceramic substrate is equal to the surface roughness of the face opposite to said wafer-putting/holding face, or a difference between the surface roughness of the wafer-putting/holding face and the surface roughness of said face opposite to said wafer-putting/holding face is 50% or less.
 2. A ceramic plate for a semiconductor producing/examining device according to claim 1, wherein said ceramic substrate is in a disc form and has a diameter of 200 mm or more and a thickness of 50 mm or less. 